note on rquired ubuntu packages + run apt update in linux workflows

.github/workflows/emu-build-all-linux.yml

@@ -82,6 +82,7 @@ jobs:
       - name: Install required packages
         shell: bash
         run: |
+          sudo apt update -y
           sudo apt install -y coreutils # echo, printf, etc...
           sudo apt install -y build-essential
           sudo apt install -y gcc-multilib # needed for 32-bit builds

.github/workflows/emu-deps-linux.yml

@@ -61,6 +61,7 @@ jobs:
     - name: Install required packages
       shell: bash
       run: |
+        sudo apt update -y
         sudo apt install -y coreutils # echo, printf, etc...
         sudo apt install -y build-essential
         sudo apt install -y gcc-multilib # needed for 32-bit builds

README.md

@@ -94,6 +94,21 @@ You can also find instructions here in [README.release.md](./post_build/README.r
 ### For Linux:
 
 * Ubuntu 22.04 LTS: https://ubuntu.com/download/desktop
+* Ubuntu required packages:
+```shell
+sudo apt update -y
+sudo apt install -y coreutils # echo, printf, etc...
+sudo apt install -y build-essential
+sudo apt install -y gcc-multilib # needed for 32-bit builds
+sudo apt install -y g++-multilib
+sudo apt install -y libglx-dev # needed for overlay build (header files such as GL/glx.h)
+sudo apt install -y libgl-dev # needed for overlay build (header files such as GL/gl.h)
+```
+*(Optional)* Additional packages
+```shell
+sudo apt install -y clang # clang compiler
+sudo apt install -y binutils # contains the tool 'readelf' mainly, and other usefull binary stuff
+```
 * Python 3.10 or above
    ```shell
    sudo add-apt-repository ppa:deadsnakes/ppa -y